The invention relates to a measured value pickup for vacuum measurements, with the pickup including a sensor and electronic circuits for supplying the sensor with voltage, signal processing, etc.
In connection with known measured value pickups for vacuum measurements there exists the particular problem that the respective sensors are small and/or sensitive, involve high costs for electrical supplies and furnish relatively small signals (for example current signals in an order of magnitude of a few .mu.-amperes). In addition to the high costs for supplying them, the costs for electronic signal processing components are also high. Finally, the systems as a whole are very complex so that additional monitoring and control systems are necessary.
Examples for vacuum measuring devices which require the described expenditures for electronic components are ionization vacuometers. These devices measure the pressure by way of the density in the number of particles. Part of the molecules or atoms present in the gas chamber are ionized. The resulting ions transfer their charge to an electrode of the system. The thus generated, very small ion current is a measure for the pressure. The formation of ions takes place either in a discharge at high electrical field intensity or by collision with electrons. Therefore, ionization vacuometers require either a high-voltage supply or a current supply for the relatively high heating current and an anode voltage. Due to the very small measurement voltages, high costs for signal processing are also required.
Another example for a vacuum measuring device including a sensor that involves particularly high supply expenses is the gas friction vacuometer. In this device, the gas friction which is a function of pressure at low gas pressures is utilized to generate a measurement signal. The measuring device employed is, for example, a steel ball which is suspended without contact in a magnetic field. This ball is caused to rotate by electromagnetic pulses. After reaching a high number of revolutions, the drive is switched off so that the number of revolutions decreases more or less rapidly under the influence of the pressure dependent gas friction. Therefore, the decrease in the number of revolutions per unit time is a measure for the existing pressure.
Finally, the sensors of partial pressure vacuum measuring devices also involve high supply costs. Their measured value pickups include an ion source, a separating system and an ion trap. Ion source and separating system (quadrupole, mass dispersive deflection field or the like) require the most varied voltages for operation; the quadrupole separating system, for example, requires a high direct voltage and a high-frequency alternating voltage.
Vacuometers of the described type offered on the market include an operating device performing operational, display, supply, control and monitoring functions. This operating device is relatively large and must be arranged where the pressure to be monitored is to be displayed and/or the associated measured values are processed further. The actual sensor, however, must be located where the recipient is located whose pressure is to be monitored. Due to less than ideal line conditions and/or extraneous interferences, the transmission of the relatively small sensor signal to the operating device without interference is not possible over any desired distance so that the prior art vacuometers can be employed only where the distance between operating device and sensor is not too great, which means that they can be employed only within limits.